1. Field of the Invention
This invention relates to the arrangement of a traction drive on the chassis of a rail-mounted forging manipulator.
2. Description of the Prior Art
Traction drives for forging manipulators commonly comprise one or more hydraulic motors, and a transmission, preferably mounted away from the hot region at the forward end of the chassis. Traction is effected by means of toothed wheels, for example spur gears or chain sprocket wheels, which mesh with fixed gear racks or chains acting as racks, in order to obtain precisely specified and controlled forward and rearward travel of the manipulator chassis. The chains are usually pin rack chains. Alternatively, gear racks or pin racks can be used. The racks are usually mounted close to the rails on which the chassis runs, to leave space for the long slidable forging tables of a forging press.
Two main arrangements are used for mounting the traction drives:
In one arrangement the traction drive is behind the rear wheels and is suspended from front and rear cross members disposed between side members of the chassis: see German Patent Specifications OS Nos. 2143669 and AS 1652815. In this arrangement, the cross members have to transmit the applied forces to the side members of the chassis, and must absorb additional bending forces. Access is difficult because the motor and sprocket wheel are between the side members of the chassis. The traction drive has to be removed from above, so that a superstructure cannot be provided on the rear part of the chassis. Because the racks are placed as close as possible to the rails, the output shafts, on the ends of which the sprockets or spur gears are mounted, project a considerable distance from the drive transmission casing and therefore have a substantial overhanging length. These shafts are therefore subject to unnecessary bending forces. The transmission of force through the cross members, and the length of the output shafts, leads to undesirable flexing or resilience with adverse effects on the accuracy of the travel and positioning of the forging manipulator. Another disadvantage is that the transmission casing must be designed to withstand the transmission of forces and the absorption of reaction shocks. Furthermore, if the manipulator is lifted in the region of the press, it will be supported only by the sprocket wheel or spur gear in the rack or rack chain, leading to the risk of breakage of the rack or the toothed wheel.
In the other common arrangement, the traction drive is suspended in front of the rear wheels of the chassis: see French Patent Specification No. 1445178, and the Journal "Metals and Materials", December 1978/January 1979, pages 28 to 31 and picture on page 29. The advantage of this is improved accessibility to the toothed wheel and the hydraulic motor or motors, since the cross member is above the drive on the chassis. A superstructure can be built above the drive, for example comprising oil tanks, pumps, and so on. However, there are still disadvantages. The cross member must transmit force from the transmission casing to the side members of the chassis, providing a very unfavourable force transmission path. The output shafts of the drive project substantially from the drive transmission casing and are therefore subject to bending. The transmission of force through the cross member, and the long projection of the output shaft, again allow flexing which impairs the accuracy of positioning the manipulator. Removal of the transmission casins is inconvenient because the toothed wheel must be lifted out of mesh. If the manipulator is lifted in the region of the forging press, the toothed wheels are lifted out of the racks and the chassis can then roll back on its rear rail wheels.